// Copyright (c) 2007, Google Inc.
// All rights reserved.
//
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// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
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// in the documentation and/or other materials provided with the
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// this software without specific prior written permission.
//
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// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
// Author: Craig Silverstein
//
// Produce stack trace.  I'm guessing (hoping!) the code is much like
// for x86.  For apple machines, at least, it seems to be; see
//    http://developer.apple.com/documentation/mac/runtimehtml/RTArch-59.html
//    http://www.linux-foundation.org/spec/ELF/ppc64/PPC-elf64abi-1.9.html#STACK
// Linux has similar code: http://patchwork.ozlabs.org/linuxppc/patch?id=8882

#include "stacktrace.h"
#include <cstdint>  // for uintptr_t
#include <cstdio>

_START_GOOGLE_NAMESPACE_

// Given a pointer to a stack frame, locate and return the calling
// stackframe, or return NULL if no stackframe can be found. Perform sanity
// checks (the strictness of which is controlled by the boolean parameter
// "STRICT_UNWINDING") to reduce the chance that a bad pointer is returned.
template <bool STRICT_UNWINDING>
static void **NextStackFrame(void **old_sp)
{
    void **new_sp = (void **)*old_sp;

    // Check that the transition from frame pointer old_sp to frame
    // pointer new_sp isn't clearly bogus
    if (STRICT_UNWINDING) {
        // With the stack growing downwards, older stack frame must be
        // at a greater address that the current one.
        if (new_sp <= old_sp)
            return NULL;
        // Assume stack frames larger than 100,000 bytes are bogus.
        if ((uintptr_t)new_sp - (uintptr_t)old_sp > 100000)
            return NULL;
    } else {
        // In the non-strict mode, allow discontiguous stack frames.
        // (alternate-signal-stacks for example).
        if (new_sp == old_sp)
            return NULL;
        // And allow frames upto about 1MB.
        if ((new_sp > old_sp)
            && ((uintptr_t)new_sp - (uintptr_t)old_sp > 1000000))
            return NULL;
    }
    if ((uintptr_t)new_sp & (sizeof(void *) - 1))
        return NULL;
    return new_sp;
}

// This ensures that GetStackTrace stes up the Link Register properly.
void StacktracePowerPCDummyFunction() __attribute__((noinline));
void StacktracePowerPCDummyFunction()
{
    __asm__ volatile("");
}

// If you change this function, also change GetStackFrames below.
int GetStackTrace(void **result, int max_depth, int skip_count)
{
    void **sp;
    // Apple OS X uses an old version of gnu as -- both Darwin 7.9.0 (Panther)
    // and Darwin 8.8.1 (Tiger) use as 1.38.  This means we have to use a
    // different asm syntax.  I don't know quite the best way to discriminate
    // systems using the old as from the new one; I've gone with __APPLE__.
#ifdef __APPLE__
    __asm__ volatile("mr %0,r1"
                     : "=r"(sp));
#else
    __asm__ volatile("mr %0,1"
                     : "=r"(sp));
#endif

    // On PowerPC, the "Link Register" or "Link Record" (LR), is a stack
    // entry that holds the return address of the subroutine call (what
    // instruction we run after our function finishes).  This is the
    // same as the stack-pointer of our parent routine, which is what we
    // want here.  While the compiler will always(?) set up LR for
    // subroutine calls, it may not for leaf functions (such as this one).
    // This routine forces the compiler (at least gcc) to push it anyway.
    StacktracePowerPCDummyFunction();

    // The LR save area is used by the callee, so the top entry is bogus.
    skip_count++;

    int n = 0;
    while (sp && n < max_depth) {
        if (skip_count > 0) {
            skip_count--;
        } else {
            // PowerPC has 3 main ABIs, which say where in the stack the
            // Link Register is.  For DARWIN and AIX (used by apple and
            // linux ppc64), it's in sp[2].  For SYSV (used by linux ppc),
            // it's in sp[1].
#if defined(_CALL_AIX) || defined(_CALL_DARWIN)
            result[n++] = *(sp + 2);
#elif defined(_CALL_SYSV)
            result[n++] = *(sp + 1);
#elif defined(__APPLE__) || (defined(__linux) && defined(__PPC64__))
            // This check is in case the compiler doesn't define _CALL_AIX/etc.
            result[n++] = *(sp + 2);
#elif defined(__linux)
            // This check is in case the compiler doesn't define _CALL_SYSV.
            result[n++] = *(sp + 1);
#else
#error Need to specify the PPC ABI for your archiecture.
#endif
        }
        // Use strict unwinding rules.
        sp = NextStackFrame<true>(sp);
    }
    return n;
}

_END_GOOGLE_NAMESPACE_
